Environment plugin permission defaults

[qwofford]

Environment plugins should assume a default permission of UID:GID and 660.

[DanielRJohnson]

See 8be2327
If None is handed to register_columns_with_file, it defaults to (UID, eGID, 0o660) instead of (None, None, None).

[Vedant1]

Closing, since Environment parent class in env.py sets UID and GID to default values, not None and None.